Currently it is known to use various domestic appliances, such as dishwashers, washing machines, showers, various sinks, et cetera, which dispense water which is heated beforehand for example by a boiler for the various domestic uses.
The appliances designed to heat the water to the temperature set by the user, such as for example boilers, burn a certain amount of fuel or use electric power, and so do washing machines or dishwashers which use their own electrical resistance heaters, the energy consumption of which is higher than the heating that can be obtained with a gas-, gas oil- or coal-fired boiler.
However, the hot water, which can reach even 90° in the case of the drain of a washing machine, 70° in the case of a dishwasher, 30° to 50° for a sink, 30° to 40° for a bathtub or shower, and 80° to 90° for a kitchen sink, once it has been used, is conveyed directly, through suitable pipes, to the soapy water drain, such water being then conveyed into a sewer drain.
Therefore, the use of these known domestic appliances requires a high level of energy resources to obtain hot water and at the same time entails the conveyance, after its use, of water which is still warm directly into the sewer drain and whose heat is thus dispersed into the environment.